Enhanced heavy oil recovery using downhole bitumen upgrading with steam assisted gravity drainage

ABSTRACT

Methods for recovery of heavy oils use selective catalytic downhole upgrading with SAGD technology. Certain embodiments include extracting heavy oil using a SAGD process and upgrading the heavy oil in a production well with a cracking catalyst. The cracking catalyst is introduced into the production well, allowing the extracted hydrocarbons to interface with the cracking catalyst to upgrade the hydrocarbons. The upgraded hydrocarbons are then separated from the cracking catalyst. This upgraded stream has a lower molecular weight, significantly reducing the viscosity of the produced hydrocarbons. A gasifier is provided to gasify a portion of the slurry containing unconverted heavy oil and cracking catalyst to produce syngas. The syngas may then be used to produce steam for use in the SAGD extraction process, improving energy efficiency of the process. Further, formation catalyst losses are avoided as the catalyst injected into the well is recovered and available for reuse.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a non-provisional application which claims benefitunder 35 USC §119(e) to U.S. Provisional Application Ser. No. 61/582,627filed Jan. 3, 2012, entitled “Enhanced Heavy Oil Recovery Using DownholeBitumen Upgrading with Steam Assisted Gravity Drainage,” which isincorporated herein in its entirety.

FIELD OF THE INVENTION

The present invention relates generally to methods and systems forenhanced recovery of heavy oils. More particularly, but not by way oflimitation, embodiments of the present invention include methods andsystems for enhancing recovery of heavy oils using selective catalyticdownhole upgrading of a portion of the heavy oil in combination withsteam-assisted gravity drainage technology.

BACKGROUND

The production of hydrocarbons from low mobility reservoirs presentssignificant challenges. Low mobility reservoirs are characterized byhigh viscosity hydrocarbons, low permeability formations, and/or lowdriving forces. Any of these factors can considerably complicatehydrocarbon recovery. Extraction of high viscosity hydrocarbons istypically difficult due to the relative immobility of the high viscosityhydrocarbons. For example, some heavy crude oils, such as bitumen, arehighly viscous and therefore immobile at the initial viscosity of theoil at reservoir temperature and pressure. Indeed, such heavy oils maybe quite thick and have a consistency similar to that of peanut butteror heavy tars, making their extraction from reservoirs especiallychallenging. As used herein, the term, “heavy oil” includes any heavyhydrocarbons having greater than 10 carbon atoms per molecule. Further,the term “heavy oil” includes heavy hydrocarbons having a viscosity inthe range of from about 100 to about 100,000 centipoise at 100° F., andan API gravity from about 5 to about 22° API; or can be a bitumen havinga viscosity less than about 100,000 centipoise, and an API gravity lessthan or equal to about 22° API.

Conventional approaches to recovering heavy oils often focus on methodsfor lowering the viscosity of the heavy oil or heavy oil mixture so thatthe heavy oil may be produced from the reservoir. Examples of methodsfor lowering the heavy oil viscosity include introducing a diluent tothe heavy oil or heating the heavy oil. Commonly used heating methodsinclude a number of technologies, such as steam flooding, cyclic steamstimulation, and Steam Assisted Gravity Drainage (SAGD), which requirethe injection of hot fluids into the reservoir. A 100° F. increase inthe temperature of the heavy oil in a formation can lower the viscosityby two orders of magnitude. Thus, heating formation heavy oils candramatically improve the efficiency of heavy oil recovery.

While diluents, such as solvents or lighter hydrocarbons introduced intoa formation, can be effective at reducing the viscosity of the heavyoils therein, solvents can be quite expensive. Indeed, not only aresolvents quite expensive, the use of diluents also suffers from costlysolvent losses (i.e. solvent lost to the formation that is notsubsequently recovered). Thus, the process economics of using diluentsare highly sensitive to both solvent cost and solvent losses. Often, theuse of solvents to recover heavy oils is prohibitively expensive.

As for the heating methods used to enhance recovery of heavy oils, thesemethods are highly disadvantageous in that they are all significantlyenergy intensive. In some cases, these thermal recovery techniques areso inefficient that they are often non-economically viable forrecovering heavy crude oil. Indeed, about 2 to 3 barrels of water musttypically be vaporized to steam for each barrel of oil produced. Notonly must the heavy oil be heated, but the entire mass in the reservoirincluding rock and sand must also be heated, thus contributing to theinefficiency of these conventional heating methods.

Not only are these energy-intensive processes often economicallyinefficient, the hydrocarbons produced are usually a lower quality crudeoil that requires upgrading either at the production site or at arefinery. Because heavy oils are so viscous, they cannot often betransported from the production site without adding diluents.

Unfortunately, due to the capital intensive nature of an upgradingfacility, upgrading facilities only become economical when used toservice large quantities of crude oil (e.g. greater than about 100,000barrels of crude oil a day). Therefore, upgrading facilities aretypically not economical for those wells producing less than about100,000 barrels of crude oil a day.

Certain conventional methods contemplate in-situ upgrading in which anupgrading catalyst is injected into a subterranean formation to allowthe crude oil therein to be upgraded. Unfortunately, this conventionalmethod suffers from the disadvantage of large catalyst losses to theformation. Also, it is difficult to control the distribution and contactduration of the catalyst in the formation to maximize the impact of thecatalyst with the heavy oil. Further, unlike surface upgradingfacilities, this method does not allow reuse of any of the upgradingcatalyst injected to the formation.

Thus, the energy inefficiencies of SAGD processes combined with thelimitations of conventional upgrading technologies limit the efficiencyunder which heavy oil can be produced. Accordingly, there is a need forenhanced heavy oil recovery methods that address one or more of thedisadvantages of the prior art.

SUMMARY

The present invention relates generally to methods and systems forenhanced recovery of heavy oils. More particularly, but not by way oflimitation, embodiments of the present invention include methods andsystems for enhancing recovery of heavy oils using selective catalystdownhole upgrading scheme in combination with steam-assisted gravitydrainage technology.

One example of a method for enhancing heavy oil recovery from asubterranean formation comprises the steps of: providing a productionwell intersecting a subterranean formation, wherein the production wellis in fluid communication with an injection well to form a well pairamong one or more steam-assisted gravity drainage production well pairsfor recovering heavy oil from a bitumen formation; (a) providing acracking catalyst; (b) heating the cracking catalyst to a catalystpre-heated temperature; (c) introducing the cracking catalyst into theproduction well at a catalyst injection point above a producinginterval; (d) allowing the heavy oil to be produced through theproduction well; (e) allowing the heavy oil to be upgraded in theproduction well in the presence of the cracking catalyst to form anupgraded mixture; wherein the catalyst pre-heated temperature issufficient to provide a reaction temperature of about 500° F. to about550° F. during step (e); (f) introducing the upgraded mixture to aseparator to separate the upgraded mixture into a hydrocarbon-enrichedstream and a catalyst slurry; (h) separating the catalyst slurry intotwo streams, a gasification feed and recovered catalyst; (i) recyclingthe recovered catalyst to the catalyst injection point; (j) introducingthe gasification feed to a gasifier to gasify the gasification feed toproduce a syngas and a waste stream; (k) producing steam using thesyngas in a steam generator for use in the one or more steam-assistedgravity drainage production well pairs; (l) introducing the steam intothe one or more steam-assisted gravity drainage production well pairs.

One example of a method for enhancing heavy oil recovery from asubterranean formation comprises the steps of: providing a productionwell intersecting a subterranean formation, wherein the production wellis in fluid communication with an injection well to form a well pairamong one or more steam-assisted gravity drainage production well pairsfor recovering heavy oil from a bitumen formation; (a) providing acracking catalyst; (b) heating the cracking catalyst; (c) introducingthe cracking catalyst into the production well at a catalyst injectionpoint above a producing interval; (d) allowing the heavy oil to beproduced through the production well; (e) allowing the heavy oil to beupgraded in the production well in the presence of the cracking catalystto form an upgraded mixture; (f) introducing the upgraded mixture to aseparator to separate the upgraded mixture into a hydrocarbon-enrichedstream and a catalyst slurry; (h) separating the catalyst slurry intotwo streams, a gasification feed and recovered catalyst; (i) recyclingthe recovered catalyst to the catalyst injection point; (j) introducingthe gasification feed to a gasifier to gasify the gasification feed toproduce a syngas and a waste stream; (k) producing steam using thesyngas in a steam generator for use in the one or more steam-assistedgravity drainage production well pairs; (l) introducing the steam intothe one or more steam-assisted gravity drainage production well pairs.

The features and advantages of the present invention will be apparent tothose skilled in the art. While numerous changes may be made by thoseskilled in the art, such changes are within the spirit of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of the present disclosure and advantagesthereof may be acquired by referring to the following description takenin conjunction with the accompanying figures, wherein:

FIG. 1 illustrates an example of an enhanced heavy oil recovery systemusing a downhole upgrading catalyst in combination with a SAGD processin accordance with one embodiment of the present invention.

While the present invention is susceptible to various modifications andalternative forms, specific exemplary embodiments thereof have beenshown by way of example in the drawings and are herein described indetail. It should be understood, however, that the description herein ofspecific embodiments is not intended to limit the invention to theparticular forms disclosed, but on the contrary, the intention is tocover all modifications, equivalents, and alternatives falling withinthe spirit and scope of the invention as defined by the appended claims.

DETAILED DESCRIPTION

The present invention relates generally to methods and systems forenhanced recovery of heavy oils. More particularly, but not by way oflimitation, embodiments of the present invention include methods andsystems for enhancing recovery of heavy oils using selective catalyticdownhole upgrading of heavy oil in combination with steam-assistedgravity drainage technology.

In certain embodiments, methods and systems for enhancing recovery ofheavy oils comprise the steps of extracting heavy oil using a SAGDprocess and upgrading the heavy oil in a production well with a crackingcatalyst. In this way, cracking catalyst is introduced into theproduction well, allowing the extracted hydrocarbons to intimatelyinterface with the cracking catalyst so as to upgrade the hydrocarbonsin the production well. The upgraded hydrocarbons thus produced areseparated from the cracking catalyst in a separator. This upgradedstream has a lower molecular weight which significantly reduces theviscosity of the produced heavy oil at similar temperatures.

A gasifier is provided to gasify a portion of the slurry that containsunconverted heavy oil and cracking catalyst. The produced syngas is thenused to produce steam for use in the SAGD extraction process. In thisway, the energy efficiency of the SAGD process is improved by leveragingsyngas produced from the gasifier to produce steam. Further, thisenhanced process avoids catalyst losses to the formation as the catalystthat is injected into the production well is recovered and available forreuse. The specific activity of the catalyst can be controlled by mixingthe recycled catalyst with fresh catalyst. Other features, embodiments,and advantages will be apparent from the disclosure herein.

Reference will now be made in detail to embodiments of the invention,one or more examples of which are illustrated in the accompanyingdrawings. Each example is provided by way of explanation of theinvention, not as a limitation of the invention. It will be apparent tothose skilled in the art that various modifications and variations canbe made in the present invention without departing from the scope orspirit of the invention. For instance, features illustrated or describedas part of one embodiment can be used on another embodiment to yield astill further embodiment. Thus, it is intended that the presentinvention cover such modifications and variations that come within thescope of the invention.

FIG. 1 illustrates an example of an enhanced heavy oil recovery systemusing a selective catalyst downhole upgrading scheme in combination witha SAGD process in accordance with one embodiment of the presentinvention. In this example, enhanced heavy oil recovery system 100comprises SAGD well pair 122, separator 130, slurry catalyst tank 140,fresh catalyst tank 150, process heater 160, gasifier 170, and steamgenerator 180.

Production well 112 and steam injection well 120 intersect subterraneanformation 105 for extracting heavy oil from production interval 114.Portions of production well 112 and steam injection well 120 togetherforms a SAGD well pair 122, which traverses through production interval114. Typically, SAGD well pairs comprise a pair of horizontal wellsdrilled into an oil reservoir, one a few meters above the other (e.g.about 4 to about 6 meters). The upper well injects steam, possibly mixedwith solvents, and the lower one collects the heated crude oil orbitumen that flows out of the formation, along with any water from thecondensation of injected steam. The basis of the process is that theinjected steam forms a “steam chamber” that grows vertically andhorizontally in the formation. The heat from the steam reduces theviscosity of the heavy crude oil or bitumen which allows it to flow downinto the lower wellbore. The steam and gases rise due to their lowdensity compared to the heavy crude oil below, ensuring that steam isnot produced at the lower production well. Production as high as 70% to80% of oil in place is common in suitable reservoirs. In this way, theSAGD process may be used to extract heavy oil for production to surface110 via production well 112. It is recognized that a plurality of SAGDwell pairs may be used to extract heavy oil from subterranean formation105 as desired.

Often, the heavy oil thus produced is of low quality and requiresadditional viscosity reduction, usually around an API of at least about19 to about 22°, to allow transportation of the heavy oil to its finaldestination. While this can be accomplished by adding diluent to theextracted hydrocarbons, this method is often not economical.Additionally, as described in the Background Section, upgradingfacilities are capital intensive and therefore may not always beeconomical, especially for smaller production wells. Accordingly, themethods herein contemplate introducing heated cracking catalyst 162 toproduction well 112 at catalyst injection point 116. In this way,extracted heavy oil may be upgraded in the presence of heated crackingcatalyst 162 as the heavy oil and cracking catalyst 162 flow throughdownhole reaction interval 118. In certain embodiments, the ratio ofheated cracking catalyst 162 to heavy oil varies from three to seven ona weight basis.

Cracking catalysts suitable for use with this invention include anycatalysts capable of upgrading the heavy oil to lighter compounds atproduction temperatures and pressures. To achieve adequate cracking attemperatures found in production systems, a high activity catalyst isrequired. Examples of suitable cracking catalysts include high surfacearea catalysts, such as, nanocatalysts. In some embodiments, thecracking catalyst includes particle sizes ranging from about 50micrometers to about 100 micrometers. In some embodiments, the particlesize of the cracking catalyst is selected to maximize surface area forenhanced upgrading reaction of the heavy oil.

Catalyst injection point 116 may be located at any distance fromproducing interval 114 to prevent catalyst loss to the formation.Examples of suitable distances include, but are not limited to, about 50feet from producing interval 114 and about 40 feet to about 100 feetfrom producing interval 114. In certain embodiments, the length anddiameter of the production well is preferably of dimensions to provide asufficient reaction residence time to allow the extracted hydrocarbonsto be sufficiently upgraded. Downhole reaction interval 118 may be anylength suitable for providing sufficient reaction residence time toallow the heavy oil to be upgraded as desired.

The main criteria for determining upgrading success are reduction inviscosity. The degree of viscosity reduction is based on the economicsof the cost of upgrading versus the decrease in cost of any diluentnecessary to allow pipeline transportation of the heavy oil. The rangeis from maximum diluent (traditional approach) to no diluent. At maximumdiluent, up to one part light condensate—natural gas liquids—may beadded to two parts bitumen.

Examples of suitable selective catalytic downhole reaction intervallengths include, but are not limited to, at least about 500 feet andlengths from about 500 feet to about 1,200 feet. Examples of suitablereaction residence times include, but are not limited to, about twoseconds to about 2 minutes to several minutes.

Upgraded mixture 129 exits subterranean formation via production well112 at surface 110. Upgraded mixture 129 comprises both upgradedhydrocarbons combined with catalyst slurry. Upgraded mixture 129 isintroduced to separator 130 to separate upgraded mixture 129 intohydrocarbon-enriched stream 132 and recovered catalyst 134. In certainembodiments, separator 130 is any process equipment suitable forseparating hydrocarbon-enriched stream 132 from recovered catalyst 134.Examples of suitable separators include, but are not limited to,fractionators, flash drums, or any combination thereof. From separator130, recovered catalyst 134 flows to optional slurry catalyst tank 140.The recovered catalyst may be split into recycled catalyst 142 a andgasification feed 144. Now that hydrocarbon-enriched stream 132 has ahigher API (i.e. a lower viscosity) than the heavy oil in-situ in theformation, hydrocarbon-enriched stream 132 may be transported to a finaldestination, for example, to storage or to a refinery for furtherprocessing.

Recycled catalyst 142 a combines with fresh catalyst 152 from freshcatalyst tank 150 to form cracking catalyst mixture 154 and is fed toprocess heater 160. In certain embodiments, process heater 160 heatscracking catalyst mixture 154 to form heated cracking catalyst 162.Process heater 160 heats heated cracking catalyst 162 to a temperatureto achieve an overall reaction temperature of about 500° F. to about550° F. In some alternative embodiments, all or a portion of recycledcatalyst 142 a may bypass process heater 160 via diverted catalyst 142b. In this way, catalyst slurry may be recycled to allow catalyst reusefor upgrading the extracted heavy oil from subterranean formation 105.This recycling of catalyst avoids the catalyst losses inherent to thoseconventional methods that inject catalyst directly into the subterraneanformations. Moreover, introducing the catalyst in the confined space ofproduction well 112 allows the catalyst to be actively concentrated onthe extracted heavy oil and further allows the reaction conditions to bemore precisely controlled or varied, which is not possible wheninjecting catalyst directly into a formation.

Returning to separator 130, gasification feed 144 comprises a portion ofrecovered catalyst 134. Gasification feed is introduced to gasifier 170.Gasification is a process that converts organic or fossil basedcarbonaceous materials into carbon monoxide, hydrogen, carbon dioxideand methane. This process is achieved by reacting material at hightemperatures (e.g. greater than about 700° C.), without combustion, witha controlled amount of oxygen and/or steam. The resulting gas mixture isoften referred to as syngas (from synthesis gas or synthetic gas) orproducer gas and is itself a fuel. One of the advantages of gasificationis that using the syngas is potentially more efficient than directcombustion of the original fuel, because it can be combusted at highertemperatures, so that the thermodynamic upper limit to the efficiencydefined by Carnot's rule is higher or not applicable. In addition, thehigh-temperature combustion refines out corrosive ash elements such aschloride and potassium, allowing clean gas production from otherwiseproblematic fuels.

Thus, gasification of gasification feed 144 in gasifier 170 producessyngas 172 and waste stream 174. Syngas 172 may be used as a fuel toproduce steam in steam generator 180 or to produce heat in processheater 160 by combusting syngas 172. Steam generator 180 may comprise adirect steam generator, an indirect steam generator, or a combinationthereof for generating steam 182. By leveraging syngas 172 for steamproduction in the SAGD process, energy savings are realized and theefficiency of the SAGD process is enhanced. Waste stream 174 is alsoproduced by gasifier 170. Waste stream 174 is typically disposed of.

In certain optional embodiments, a portion of syngas 170 may be divertedfor use in process heater 160 to reduce energy requirements needed toheat cracking catalyst mixture 154 to form heated cracking catalyst 162.This use of syngas 170 in process heater 160 reduces the overall energyrequired to heat cracking catalyst mixture 154 and therefore furthereconomizes energy usage of the upgrading process.

A higher quality upgraded product can be produced by separating thehydrogen from the syngas and directing it to the well bore. Introducinghydrogen in the catalytic upgrading will result in a more stable productthan with non-hydrogen upgrading.

It is recognized that any of the elements and features of each of thedevices described herein are capable of use with any of the otherdevices described herein without limitation. Furthermore, it isrecognized that the steps of the methods herein may be performed in anyorder except unless explicitly stated otherwise or inherently requiredotherwise by the particular method.

Therefore, the present invention is well adapted to attain the ends andadvantages mentioned as well as those that are inherent therein. Theparticular embodiments disclosed above are illustrative only, as thepresent invention may be modified and practiced in different butequivalent manners apparent to those skilled in the art having thebenefit of the teachings herein. Furthermore, no limitations areintended to the details of construction or design herein shown, otherthan as described in the claims below. It is therefore evident that theparticular illustrative embodiments disclosed above may be altered ormodified and all such variations and equivalents are considered withinthe scope and spirit of the present invention. Also, the terms in theclaims have their plain, ordinary meaning unless otherwise explicitlyand clearly defined by the patentee.

What is claimed is:
 1. A method for enhancing heavy oil recovery from asubterranean formation comprising the steps of: (a) providing aproduction well intersecting a subterranean formation, wherein theproduction well is in fluid communication with an injection well to forma well pair among one or more steam-assisted gravity drainage productionwell pairs for recovering heavy oil from a bitumen formation; (b)providing a cracking catalyst; (c) heating the cracking catalyst to acatalyst pre-heated temperature; (d) introducing the cracking catalystinto the production well at a catalyst injection point above a producinginterval; (e) allowing the heavy oil to be produced through theproduction well; (f) allowing the heavy oil to be upgraded in theproduction well in the presence of the cracking catalyst to form anupgraded mixture; (g) wherein the catalyst pre-heated temperature issufficient to provide a reaction temperature of about 500° F. to about550° F. during step (f); (h) introducing the upgraded mixture to aseparator to separate the upgraded mixture into a hydrocarbon-enrichedstream and a catalyst slurry; (i) separating the catalyst slurry intotwo streams, a gasification feed and recovered catalyst; (j) recyclingthe recovered catalyst to the catalyst injection point; (k) introducingthe gasification feed to a gasifier to gasify the gasification feed toproduce a syngas and a waste stream; (l) producing steam using thesyngas in a steam generator for use in the one or more steam-assistedgravity drainage production well pairs; (m) introducing the steam intothe one or more steam-assisted gravity drainage production well pairs.2. The method of claim 1 further comprising the step of heating at leasta portion of the recovered catalyst after step (i) and before step (j).3. The method of claim 2 wherein a portion of the syngas produced instep (j) is used to heat the recovered catalyst.
 4. The method of claim1 wherein the injection point is about 40 to about 100 feet above theproducing interval.
 5. The method of claim 1 wherein the production wellhas a length of at least about 500 feet or from about 500 to about 1,200feet.
 6. The method of claim 1 wherein the production well has a lengthsufficient to provide a reaction residence time from the catalystinjection point to the surface of about 20 seconds to about 2 minutes.7. The method of claim 1 wherein the cracking catalyst is high activity,high surface area catalyst.
 8. The method of claim 7 wherein thecracking catalyst comprises a nanocatalyst.
 9. The method of claim 1wherein the ratio of cracking catalyst introduced into the productionwell to the heavy oil produced through the production well is aboutthree to about seven on a weight basis.
 10. The method of claim 1wherein the cracking catalyst has a particle size of about 50 μm toabout 100 μm
 11. The method of claim 1 wherein the hydrocarbon-enrichedstream has an API from about 5° to about 22°.
 12. The method of claim 1wherein the separator is a flash tower or a fractionator.
 13. The methodof claim 1 wherein the separator comprises a fractionator.
 14. Themethod of claim 1 wherein the one or more steam-assisted gravitydrainage production well pairs comprises a plurality of steam-assistedgravity drainage production well pairs.
 15. The method of claim 1wherein the steam generator is a direct steam generator or an indirectsteam generator; wherein the steam is generated in step (1) bycombustion of the syngas.
 16. A method for enhancing heavy oil recoveryfrom a subterranean formation comprising the steps of: (a) providing aproduction well intersecting a subterranean formation, wherein theproduction well is in fluid communication with an injection well to forma well pair among one or more steam-assisted gravity drainage productionwell pairs for recovering heavy oil from a bitumen formation; (b)providing a cracking catalyst; (c) heating the cracking catalyst; (d)introducing the cracking catalyst into the production well at a catalystinjection point above a producing interval; (e) allowing the heavy oilto be produced through the production well; (f) allowing the heavy oilto be upgraded in the production well in the presence of the crackingcatalyst to form an upgraded mixture; (g) introducing the upgradedmixture to a separator to separate the upgraded mixture into ahydrocarbon-enriched stream and a catalyst slurry; (h) separating thecatalyst slurry into two streams, a gasification feed and recoveredcatalyst; (i) recycling the recovered catalyst to the catalyst injectionpoint; (j) introducing the gasification feed to a gasifier to gasify thegasification feed to produce a syngas and a waste stream; (k) producingsteam using the syngas in a steam generator for use in the one or moresteam-assisted gravity drainage production well pairs; (l) introducingthe steam into the one or more steam-assisted gravity drainageproduction well pairs.
 17. The method of claim 16 further comprising thestep of heating at least a portion of the recovered catalyst after step(h) and before step (i);
 18. The method of claim 17 wherein a portion ofthe syngas produced in step (j) is used to heat the recovered catalyst.